Both gain and loss of function studies indicate that proneural bHLH transcription factors play important and diverse roles in patterning neurogenesis in the developing embryo. These genes share common abilities to drive general aspects of neuronal differentiation as well as distinct abilities to drive neuronal subtype specific properties within competent progenitor populations. These convergent and divergent aspects of individual proneural bHLH function likely depend on distinct patterns of downstream target regulation. What are these patterns and how are they regulated by individual proneural bHLH transcription factors? The goal of the current study is to compare patterns of downstream target activation in response to two members of the Xenopus proneural bHLH gene family, the achaete-scute related gene, Xash1, and the atonal related gene, XNgnr1. We will then use these distinct patterns of target activation to probe the structural correlates of individual proneural bHLH function. Finally, we will examine the role of protein:protein interactions in modulating Xash1 and XNgnr1 induced target regulation, providing insight into the role of accessory factors in shaping individual proneural bHLH function